Three-dimensional nickel vanadium layered double hydroxide nanostructures grown on carbon cloth for high-performance flexible supercapacitor applications

Insights into the Morphological Effects of 1D, 2D, and 3D CoV-Layered Double Hydroxides on Their Electrochemical Performance in Supercapacitors

In this study, bimetallic cobalt-vanadium-based layered double hydroxide (CoV-LDH) systems were developed by varying the Co/V molar ratios (1:1 and 2:1) and hydrothermal temperatures (120 and 180 °C). Structural analysis by X-ray diffraction (XRD), Raman, and Fourier-transform infrared (FTIR) spectroscopy indicated the successful formation of CoV-LDH with a unique structure and lattice distortions, reflecting the influence of both the metal concentrations and temperature on the crystal and chemical structures of the developed bimetallic systems. Similarly, the field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) images revealed a flaky 2D nanosheet-like structure for the bimetallic CoV-LDH with a 1:1 ratio prepared at 120 °C (CVL1-120), whereas one-dimensional (1D) and three-dimensional (3D) morphologies were observed for other bimetallic CoV-LDH systems prepared with a different molar ratio (2:1) and/or temperature (180 °C). Electrochemical analysis performed in a three-electrode setup demonstrated a specific capacitance of 314.4 F g-1 at 1 A g-1 current density for CVL1-120, which is ∼4.5 and 5.2 times higher than those of monometallic Co and V-LDH, respectively. In addition, CVL1-120 exhibited an excellent capacitance retention of ∼97% over 5000 charge-discharge cycles with 100% Coulombic efficiency at 10 A g-1. Furthermore, the developed asymmetric device delivered an energy density of 36.5 Wh kg-1 and a power density of 1208.2 W kg-1. This enhanced performance of CVL1-120 was attributed to its two-dimensional (2D) flaky structures, with rich intercalated ions serving as electroactive sites, facilitating enhanced charge storage efficiency and improved stability, making it suitable as an electrode material for sustainable supercapacitors.

A geopolymer membrane for application in a structural mechanics and energy storage difunctional supercapacitor

A structural mechanics and energy storage difunctional supercapacitor based on a geopolymer membrane injected with a 0.5 M Na2SO4 electrolyte and a pseudocapacitive electrode Mn7O13 is designed and assembled. The geopolymer membrane is prepared as a structural electrolyte with metakaolin and alkaline activator solution. The wide channels in the geopolymer matrix provide paths for ion movement. The Mn7O13 electrode is prepared by different hydrothermal treatments at different temperatures and times, and assembled with activated carbon and a geopolymer with different moduli to form a difunctional supercapacitor. The results show that the electrode sample annealed at 300 °C for 45 min after hydrothermal treatment at 160 °C for 24 h exhibits the best comprehensive performance. The specific capacitance of the electrode is 175.5 F g-1 (2392.6 F m-2) at 1 A g-1, and the specific capacitance of the difunctional structure supercapacitor assembled with a geopolymer with a modulus of 1.2 and cured for 28 days is 144.12 F g-1 (1960.0F m-2) at 1 A g-1 under 15 MPa.

Growth mechanisms of monolayer hexagonal boron nitride (h-BN) on metal surfaces: theoretical perspectives

Two-dimensional hexagonal boron nitride (h-BN) has appeared as a promising material in diverse areas of applications, including as an excellent substrate for graphene devices, deep-ultraviolet emitters, and tunneling barriers, thanks to its outstanding stability, flat surface, and wide-bandgap. However, for achieving such exciting applications, controllable mass synthesis of high-quality and large-scale h-BN is a precondition. The synthesis of h-BN on metal surfaces using chemical vapor deposition (CVD) has been extensively studied, aiming to obtain large-scale and high-quality materials. The atomic-scale growth process, which is a prerequisite for rationally optimizing growth circumstances, is a key topic in these investigations. Although theoretical investigations on h-BN growth mechanisms are expected to reveal numerous new insights and understandings, different growth methods have completely dissimilar mechanisms, making theoretical research extremely challenging. In this article, we have summarized the recent cutting-edge theoretical research on the growth mechanisms of h-BN on different metal substrates. On the frequently utilized Cu substrate, h-BN development was shown to be more challenging than a simple adsorption-dehydrogenation-growth scenario. Controlling the number of surface layers is also an important challenge. Growth on the Ni surface is controlled by precipitation. An unusual reaction-limited aggregation growth behavior has been seen on interfaces having a significant lattice mismatch to h-BN. With intensive theoretical investigations employing advanced simulation approaches, further progress in understanding h-BN growth processes is predicted, paving the way for guided growth protocol design.

Emerging carbonate anion intercalated- ZnCr-layered double hydroxide/vanadium carbide nanocomposite: Sustainable design strategies based on disposal electrochemical sensor for diethofencarb fungicide monitoring

Diethofencarb (DFC) is widely used in agriculture to fight against plant fungal attacks and enhance food crop production. On the other hand, the National food safety standard has set the overall maximum residual limit (MRL) of DFC to be 1 mg/kg. Hence it becomes essential to limit their usage, and it is vital to quantify the amount of DFC present in real-life samples to safeguard the health and environmental well-being. Here, we introduce a simple hydrothermal procedure for preparing vanadium carbide (VC) anchored by ZnCr-LDH. The sustainably designed electrochemical sensor for the detection of DFC portrayed high electro-active surface area, conductivity, rapid-electron transport ratio, and high ion diffusion parameters. The obtained structural and morphological information confirms the enriched electrochemical activity of the ZnCr-LDH/VC/SPCE towards DFC. The ZnCr-LDH/VC/SPCE electrode has displayed exceptional characteristics with DPV resulting in a vast linear response (0.01-228 μM), and lower LOD (2 nM) with high sensitivity. Real-sample analysis was carried out to demonstrate the specificity of the electrode with an acceptable recovery in both water (±98.75-99.70%) and tomato (±98.00-99.75%) samples.

Regeneration study of MB in recycling runs over nickel vanadium oxide by solvent extraction for photocatalytic performance for wastewater treatments

Recently, researchers are concentrating on the synthesis of composite materials to enhance the efficiency of the materials in various applications. In this work, nickel vanadium oxide (NiV₂O₆) nanocomposite material is prepared via two methods and the prepared samples have been characterized with basic studies to analyse the effect of preparation method and the reaction time. The XRD studies reveal a polycrystalline growth in both the methods. The broad XRD peaks obtained for samples prepared via hydrothermal method suggests the size reduction and 1D nanostructure formation. The SEM analysis shows the formation of 1D structures in hydrothermal and 3D microsphere structures in solvothermal methods. The possible formation mechanism behind this formation has been discussed in this manuscript. The FTIR peaks in the fingerprint region confirm the formation and vibration of metal-oxygen bonds. The large optical bandgap values obtained from Tauc plot again confirms the formation of nanostructures of the synthesized samples. The photocatalytic activity of nickel vanadium oxide on methylene blue dye under halogen light were performed and, the recyclability of the sample is investigated. It was found from the photocatalytic spectrum that, the samples prepared from both the methods shows a degradation efficiency of more than 80% within 150 min. It was confirmed that the prepared NiV₂O₆ photocatalyst samples does not lose their degradation ability even after five cycles of repeated usage.

Cobalt vanadium chalcogenide microspheres decorated with dendrite-like fiber nanostructures for flexible wire-typed energy conversion and storage microdevices

The increasing energy demand for next-generation portable and miniaturized electronics has drawn tremendous attention to develop microscale energy storage and conversion devices with light weight and flexible characteristics. Herein, we report the preparation of flower-like cobalt vanadium selenide/nickel copper selenide (CoVSe/NiCuSe) microspheres with three-dimensional hierarchical structure of micropore growth on copper wire for a flexible fiber microsupercapacitor (microSC) and overall water splitting. The CoV-LDH microspheres are anchored on the dendrite-like NiCu nanostructured Cu wire using a hydrothermal method (CoV-LDH/NiCu@CW). The sulfidation and selenization of CoV-LDH/NiCu was carried out through the ion-exchange reaction of OH^- with sulfide and selenide ions to obtain CoVS/NiCuS@CW and CoVSe/NiCuSe@CW electrodes, respectively. Benefitting from the unique structure, the flower-like CoVSe/NiCuSe@CW microspheres exhibit better electrochemical performance compared with other as-prepared fiber-shaped electrodes. As an electrode active material for microSC, CoVSe/NiCuSe microspheres exhibit a specific capacitance of 35.40 F cm^-3 at 4 mA cm^-2, and maintain 281.25 F cm^-3 even at a high current density of 83 mA cm^-2, indicating outstanding charge storage capacitance and excellent rate capability. Moreover, the assembled flexible solid-state asymmetric microSCs based on flower-like CoVSe/NiCuSe microspheres-coated Cu wire as the positive electrode and polypyrrole/reduced graphene oxide-coated carbon fiber as the negative electrode manifests a maximum energy density of 20.17 mW h cm^-3 at a power density of 624.32 mW cm^-3 and remarkable cycling stability (96.7% after 5000 cycles) with good mechanical stability. As an electrocatalyst for oxygen and hydrogen evolution reactions in alkaline medium, the CoVSe/NiCuSe electrode delivers an overpotential of 297 mV and 165 mV at 100 mA cm^-2. Furthermore, the CoVSe/NiCuSe-based electrolysis cell for overall water splitting presents a low cell voltage (1.7 V at 50 mA cm^-2) as well as high durability.

Oxygen-defect-rich 3D porous cobalt-gallium layered double hydroxide for high-performance supercapacitor application

In this work, oxygen-defect-rich, three-dimensional (3D) cobalt-gallium layered double hydroxides (Co_0.50-Ga_0.50-LDH) assembled by porous and ultrathin nanosheets are prepared by a simple one-step strategy. Briefly, an aqueous solution containing Co²⁺ and Ga³⁺ is quickly pouring into the aqueous solution of hexamethylenetetramine, the state-of-the-art LDH was obtained followed by a mild and fast hydrothermal reaction. This mild and rapid synthesis strategy introduces a large number of pores into the ultrathin LDH nanosheets, resulting in a high concentration of oxygen vacancies in the Co_0.50-Ga_0.50-LDH, and the concentration of oxygen vacancies can be arbitrarily modulated, which has been corroborated by X-ray photoelectron spectroscopy and electron spin resonance measurements. The synergistic effect of the oxygen vacancy and the introduced Ga ions in the LDH nanosheets enhances the adsorption of the LDH nanosheets on OH^-, endowing Co_0.50-Ga_0.50-LDH with outstanding performance for the supercapacitor application. Co_0.50-Ga_0.50-LDH offers a high specific capacity (0.62C·cm^-2) at 10 mV·s^-1 and extraordinary cycling stability. An aqueous asymmetric supercapacitor (ASC) constructed with Co_0.50-Ga_0.50-LDH and activated carbon (AC) materials exhibits high energy density and a long lifespan. This result encourages the wide application of porous ultrathin LDH nanosheets in energy storage, catalysis and light response.

Advances in the design and application of transition metal oxide-based supercapacitors

In the last years, supercapacitors (SCs) have been proposed as a promising alternative to cover the power density deficiency presented in batteries. Electrical double-layer SCs, pseudocapacitors, and hybrid supercapacitors (HSCs) have shown very attractive features such as high-power density, long cycle life, and tunable specific capacitance. The advances of these energy storage devices made by transition metal oxides (TMOs) and their production in pseudocapacitors and HSCs depend on chemical composition, crystalline structure, morphology, theoretical capacitance, and oxidation states. In this way, this critical review considers several metal oxides (RuO2, MnO2, V2O5, and Co3O4) and their different configurations with diverse carbon-based materials. Energy storage mechanisms and fundamental principles to understand the promising effect of metal oxides in SCs devices are thoroughly described. Special attention as regards to the energy storage mechanisms relative to the specific capacitance values is presented in the reviewed articles. This review envisages the TMO as a key component to obtain high specific capacitance SCs.

Nickel-vanadium layered double hydroxide nanosheets as the saturable absorber for a passively Q-switched 2 µm solid-state laser

Nickel-vanadium (NiV)-layered double hydroxide (LDH) was fabricated into a novel saturable absorber (SA) by the liquid phase exfoliation method and utilized as the laser modulator for the first time, to our best knowledge. We investigated a passive Q-switched Tm:YAG ceramic laser at 2 µm with the NiV-LDH SA. Under an absorbed pump power of 7.2 W, the shortest pulse width of 398 ns was obtained with an average output power of 263 mW and a pulse repetition frequency of 101.8 kHz, corresponding to a single pulse energy at 2.30 µJ. The results indicate that the NiV-LDH SA has great research potential in the field of laser modulation.

Zn-Al Layered Double Hydroxide Film Functionalized by a Luminescent Octahedral Molybdenum Cluster: Ultraviolet-Visible Photoconductivity Response

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn₂Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low-cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo₆ cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo₆ cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.

Recent Progress in Two-Dimensional Layered Double Hydroxides and Their Derivatives for Supercapacitors

High-performance supercapacitors have attracted great attention due to their high power, fast charging/discharging, long lifetime, and high safety. However, the generally low energy density and overall device performance of supercapacitors limit their applications. In recent years, the design of rational electrode materials has proven to be an effective pathway to improve the capacitive performances of supercapacitors. Layered double hydroxides (LDHs), have shown great potential in new-generation supercapacitors, due to their unique two-dimensional layered structures with a high surface area and tunable composition of the host layers and intercalation species. Herein, recent progress in LDH-based, LDH-derived, and composite-type electrode materials targeted for applications in supercapacitors, by tuning the chemical/metal composition, growth morphology, architectures, and device integration, is reviewed. The complicated relationships between the composition, morphology, structure, and capacitive performance are presented. A brief projection is given for the challenges and perspectives of LDHs for energy research.